1. Field of the Invention
The present invention relates to a prefilled syringe and, more particularly, to a pre-filled syringe which is substantially free from elution of any lubricant such as silicone oil, and which is small in sliding resistance between a syringe barrel and a plunger to be reciprocated within a bore of the barrel.
2. Description of the Prior Art
There have been known prefilled syringes, i.e., syringes of which a barrel is previously filled with a liquid medicament and which is so designed as to administer the liquid medicament by fitting a hypodermic needle over a tip of the barrel after removing a hermetic seal from the tip of the barrel. In such a prefilled syringe, the barrel filled with a liquid medicament is generally sealed at one end by a rubber gasket and at the other end or a needle-connecting portion by a rubber plate. The needle-connecting portion is covered and sealed by a cap fitted thereon to ensure the sterility of the contents.
However, such prefilled syringes of the prior art have a serious problem for use in infusion since additives such as sulfur, vulcanization accelerators or impurities elute in the liquid medicament from the rubber plates or rubber gaskets used as the sealing members during storage of the syringes.
The above problem of the prefilled syringe of the prior art may be solved by use of a syringe, proposed in examined Japanese Utility model publication No. 55-32602, comprising a barrel made of glass and a sealing member of which surfaces to be contacted with a liquid medicament are coated or covered with a thin film of a plastic material other than fluoroplastics. However, such a syringe has a problem that the resin coated sealing member does not slide smoothly since the barrel is made of glass. Although this problem can be overcome by use of a sealing member or gasket coated with or made of fluoroplastics since fluoroplastics have a good sliding property, such sealing members or gaskets are poor in liquid-tightness and airtightness when combined with the glass barrels.
For the above reasons, disposable syringes widely used today are those employing a barrel made of plastics. When the plastic barrel is combined with a gasket made of plastics other than fluoroplastics, it is required to apply a lubricant such as silicone oils on sliding surfaces of the gasket since increase in liquid-tightness and airtightness between the gasket and barrel causes a decrease in slidability of the gasket. However, silicone oil is a foreign substance for the medicament to be administered and causes contamination of the medicament due to elution of fine particles.
To solve such problems, it has been proposed in examined Japanese utility model publication No. 5-34669 to use a gasket of which all the surfaces to be in contact with a liquid medicament and to be slid on the inner wall of the barrel are covered with a thin film of a plastic material selected from the group consisting of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer and very high polymeric polyethylene and which has a length of a contacting surface between a peripheral portion of the gasket and the inner wall of the barrel being limited within a certain range.
Although the gaskets disclosed in examined publication No. 5-34669 provide no problem when used for the ordinary syringes, they causes problems in liquid-tightness and airtightness when used for prefilled syringes. For example, if the plunger is pressed hard during storage, the liquid medicament may leak out from the syringe different from the close contact between the elastic gasket and barrel.